Magnesiohögbomite-6N12S, Mg5Al11TiO23(OH), a new högbomite-group mineral from the DeWitts Corners, Ontario, Canada

Abstract

The new hogbomite-group mineral magnesiohogbomite-6N12S, ideally Mg5Al11TiO23(OH), was found in calcite "vein-dikes" at the DeWitts Corners occurrence, lots 10 and 11, concession 1, Bathurst Township, Ontario, Canada. It forms tabular and short-prismatic crystals up to 5 mm in size. The major forms are pinacoid {0001} and hexagonal pyramid {111}, sometimes modified by hexagonal prism {110}. The associated minerals are magnesiohogbomite-2N3S, spinel, corundum, diopside, magnesio-hastingsite, pargasite, clinochlore and calcite. Magnesiohogbomite-6N12S is dark brown to black with brown streak and vitreous lustre. It has no cleavage and its fracture is uneven. The Mohs hardness is 61/2. D-calc is 3.87 g/cm(3). The infrared spectrum is reported. The composition (wt.%) is MgO 13.09, ZnO 0.46, FeO 11.91, Fe2O3 6.84, Al2O3 62.70, TiO2 4.44, H2O 0.99, total 100.43. The empirical formula calculated on the basis of 17 cations, excluding H+, is (Mg2.95Fe1.512+Al0.49Zn0.05)(Sigma 5)(Al10.71Fe0.783+Ti0.51)(Sigma 12)O-23(OH). The simplified formula is (Mg,Fe)(5)(Al,Fe,Ti)(12)O-23(OH). The mineral is trigonal, Rm, a = 5.7194(2), c = 83.069(5) angstrom, V = 2353.3(2) angstrom (3) and Z = 6. The strongest reflections of the powder X-ray diffraction pattern [d,angstrom (I)(hkl)] are: 2.921(26)(0.1.23), 2.863(49)(110), 2.687(29)(0.1.26), 2.547(31)(0.1.) and 2.434(100)(1.1.18). The crystal structure was solved and refined from single-crystal X-ray diffraction data to R-1 = 0.022. It is composed of alternating spinel (S) and nolanite (N) modules in the sequence 3 x (NSSNSS). The sequence of cubic 'c' and hexagonal 'h' closed-packed oxygen layers is 3 x (cccccchcccch). It is the first polysome in the hogbomite supergroup with such a sequence.